No, I always carry the spare and only change it if the conditions are tough. This morning with an 18mph headwind I had to change it. I had 37% left of the big one and 46% of the smaller one. The ride home with same tailwind I will probably just use the big one and have around 35% left or thereabouts. In the past with just the smaller battery I wouldn't have bothered riding in given the conditions (unpleasantly slow slog).